So far, the improvement of efficiency in a generator has been big problems in the requirement of energy saving. In the structure of the generator, electrical magnet is used for a rotor mainly, which is produced magnetic force by flowing current amount in a coil installed in the rotor. They know well that the efficiency is improved on the generator by use of a permanent magnet rotor because it is no need to use a current for producing magnetic force. However it has been difficult to use the permanent magnet (PM) generator for such as automotive vehicle driven many electric equipments by constant voltage because the generated voltage is changed up and down as generator speed change. The reason is that the magnetic force must be reduced to smaller value to maintain constant voltage at higher speed however the magnetic force can't be changed.
However many researchers are making effort to develop the PM generator to get constant voltage even if the speed is changed. Then, AC electric power is changed to DC current for a while, the DC current is switched by high frequency and the width of switching pulse is controlled to meet a voltage set in advance which is so called DC-DC converter or a phase controlled converter. The system is very expensive, large size, and low efficiency because of using large size of transistor for letting flow all of large current amount generated by the generator.
Namely, as the structure is very simple and generated power is very big in spite of small size due to very strong magnetic force, then PM generators are used for automotive and wind turbine and those have been increasing recently. In the PM generator, the motor can respond to the change of voltage even if the motor use the electric power generated in PM generator, however it is need to control voltage constantly in the case of using electric power for many electric equipments and connecting a storage battery. Many researchers have carried out to research how to control the voltage constantly in PM generator, and the method of controlling the voltage constantly used switching regulator was developed by GM however the system had big problems such as large size of controller, expensive and low efficiency.
An inverter for driving motor is used for a hybrid and an electric vehicle, the inverter system is used for the phase controlled converter in the popular systems in order to control the voltage constantly. A controller of the phase controlled converter control the voltage by cutting a waveform of electric power, then the overlap interval between the waveform of current and voltage is changed, as the result a power factor of load is reduced that is the problem of the system. In order to make the voltage constantly, the electric voltage should be chopped in the switching regulator which is used big size of power transistors, as the result the system was increased in the size, cooling system and cost. It is easy to break down much more by larger current flow into the power transistor. Because the flow of larger current amount make the temperature of the transistor raise, high voltage make an insulation between emitter and collector of a transistor break down, therefore, the smaller flowing current amount into the transistor is, the better and the cheaper, the system become.
For example, the voltage has to be reduced at high revolution speed, and has to be increased at low revolution speed in the generator with permanent magnet rotor used for a hybrid vehicle and an electric vehicle. When the converter is controlled the voltage, it is need to use a back chopper circuit or a boost chopper circuit and the controller become very complicate and expensive. On the other hand, the spike of current sometimes produced when the electric power was chopped and the spike pull the trigger of obstacle in a radio wave then the countermeasure of noise become very difficult problems.
The methods of reducing the magnetic force of permanent magnet when the rotor speed increased were studied by many researchers. For example, the controllers used reactive power were developed, which was needed big size of a converter and a reactor, on the other hand, generators wound coils in opposite directions in addition to power coil in parallel were developed, which was no need mechanical control systems and the structure was simple because of small number of parts, having reliability and the excellent control-ability of voltage in power coil, they said. Prior PM generator is composed of stator with winding coils, rotor mounted permanent magnet pieces and control coil supplied current from inverter and the current flowing into the control coil produce magnetic force in optically direction in order to reduce magnetic force to flow into stator and the voltage, which is disclosed in Japanese Patent Application Laid-Open Publication No. 2004-320972.
Furthermore, the generator realized high efficiency was proposed. Prior generator is consisted of stator with winding coil and rotor having permanent magnet pieces and iron cores then controller makes the magnetic force reduce by using reluctance power which is produced the magnetic force on non-symmetrical position disclosed in Japanese Patent Application Laid-Open Publication No. 2003-245000.
Other patent was opened that is consisted of rotor mounted permanent magnet pieces, stator with coils, and secondary magnetic coils set up in a right angle against the circuit of PM flux to control voltage or current of the power disclosed in Japanese Patent Application Laid-Open Publication No. 2006-529076.
Furthermore, a winding coil of stator is formed of a power coil wound by smaller in the number of winding, a control coil with larger in the number of winding and a solenoid coil are connected in series and a switch is provided between the power coil and control coil and a controller is increased a current flowing in control coil when the voltage of power coil is higher than a voltage set in advance, and the controller reduce the current when the voltage is lower than the voltage set in advance which is disclosed in Japanese Patent Registration No. 4227189.
However it is very difficult to weaken magnetic force of permanent magnet in response to increasing rotor revolution speed to the higher by using the methods mentioned above and those technologies have not realized in practical use.
On the other hand, DC-DC converter is used for hybrid vehicles, in the system, DC electric power rectified AC current from the generator is chopped by controller and it is transferred to DC power having a constant voltage set in advance furthermore the DC power is changed to AC power by using a inverter. However those were disturbed by complicated structure and large size of the system to be diffused them in the automotive market.
Particularly, the power factor of load is reduced when the voltage is reduced by phase control systems which are used in hybrid vehicles and an efficiency of recovering brake energy is reduced. On the other hand, energy problems become worse recently, and the consumption of electric energy in conventional vehicles increase rapidly and about 50% efficiency in the Lundell type generator has not permitted yet in conventional vehicles. As the result, a generator having simple structure and simple and certain controller is required strongly in the social situation.
The generator with stator wound two kind of coils and one side of coil was used for controlling magnetic force by flowing the current to produce magnetic force in opposed direction were developed by many researchers. In order to reduce the magnetic flux of PM force which flows into stator, the magnetic flux produced by current flowing from an inverter need to be similar shapes to PM flux, however those techniques were very difficult. Furthermore, those electric magnetic flux opposed to PM flux makes the magnetic force of PM material reduce and they suffered with the trouble of generator.